1. Field of the Invention
The present invention relates to a power plant and transmission arrangement suited for rotary wing aircraft and, more particularly, to a power plant and transmission arrangement comprising an engine integrated with a transmission.
2. Description of the Prior Art
As seen in FIG. 1, conventional helicopter power plants typically comprise an engine 10 with a reduction gearbox 12 mounted thereto as a modular unit. The engine 10 and the reduction gearbox 12 are conjointly mounted to a helicopter frame 14 and coupled to a main transmission 16 via a flexible coupling and drive shaft arrangement 18. The main transmission 16 is mounted on the helicopter frame 14 separately from the reduction gearbox 12 and is drivingly connected to a rotor mast 20, a tail rotor (not shown) and auxiliary equipment (not shown) of the helicopter in order to transmit power thereto. Alternatively, it has been proposed, as seen in FIG. 2, to suppress the reduction gearbox at the output of the engine 10xe2x80x2 and to couple the same to the main transmission 16xe2x80x2 only via the clutch and coupling shaft arrangement 18xe2x80x2.
Such arrangements wherein the transmission 16/16xe2x80x2 is mounted to the helicopter frame 14/14xe2x80x2 separately from the engine 10/10xe2x80x2 has in the past been found necessary to adequately support the loads of the rotor mast 20/20xe2x80x2 and dampen the vibrations thereof. However, one drawback associated with power plant and transmission arrangement of the type described above resides in the fact that the coupling shaft has to be fairly long for compensating even slight longitudinal and angular displacements of the main transmission, thereby negatively affecting the helicopter stability due to the substantial spacing between the engine center of gravity and the rotor mast of the helicopter.
Accordingly, attempts have been made to reduce the required length of the coupling shaft. For instance, U.S. Pat. No. 4,899,959 issued on Feb. 13, 1990, to Weiller, discloses a helicopter power plant and transmission arrangement wherein the length of the coupling shaft joining the main transmission to the engine is minimized by the provision of a flex coupling between the engine and the reduction gearbox. One disadvantage associated to the use of flexible couplings is that they significantly limit the speed at which the coupling shaft may be driven and consequently the engine speed of the helicopter.
Therefore, there is a need for a new helicopter power plant and transmission arrangement adapted to improve the stability and handling characteristics of a helicopter without significantly limiting engine speed thereof.
It is therefore an aim of the present invention to provide a new rotary wing aircraft power plant and transmission arrangement adapted to improve aircraft stability by placing the center of gravity of the power plant closer to a main rotor mast of the rotary wing aircraft.
It is also an aim of the present invention to provide a new rotary wing aircraft power plant and transmission arrangement having a reduced overall weight.
It is a further aim of the present invention to provide a rotary wing aircraft power plant and transmission arrangement wherein the transmission is combined into a single module with the power plant.
It is a still further aim of the present invention to provide a rotary wing aircraft power plant and transmission arrangement which is relatively economical to manufacture.
Therefore, in accordance with the present invention, there is provided a power plant and transmission arrangement for a rotary wing aircraft having a frame, comprising engine means for generating mechanical power, the engine means including a casing, and a transmission directly connected to the engine means for transmitting power from the engine means to driven components of the rotary wing aircraft, the transmission including a housing, the housing and the casing being integrated together to ensure that the engine means and the transmission act as a single unit with respect to the frame. By so integrating the engine means to the transmission, it becomes possible to reduce the spacing between the center of gravity of the engine means and the rotor mast of the rotary wing aircraft, thereby advantageously improving the handling characteristics of the rotary wing aircraft.